The field of the disclosure relates generally to flight control systems and, more specifically, to a flight control module utilizing a synthetic inertial glideslope deviation.
Many known aircraft feature an automated landing system that controls the aircraft during landing. Automated landing systems have become increasingly more common and are frequently relied on for both instrument landings under instrument flight rules (IFR) and landings performed under visual flight rules (VFR). Known automated landing systems utilize various receivers, such as multi-mode receivers (MMRs), for example, to receive guidance signals transmitted from the ground. Such guidance signals may include, for example, instrument landing system (ILS) signals, global positioning service (GPS) landing system (GLS) signals, and/or microwave landing system (MLS) signals. The guidance signals inform the aircraft of its position relative to a desired vertical and lateral path to the runway and through roll-out after touchdown. The desired vertical path is referred to as the glideslope and the lateral path is referred to as the localizer. The glideslope is typically defined as a 3° descent with a desired intercept with the ground at 1000 feet beyond the runway threshold. The localizer guides the aircraft to the runway centerline.
The guidance signals transmitted from the ground are received by an on-board antenna and routed to redundant MMRs. Each MMR computes a localizer deviation and a glideslope deviation that are routed to a flight control module that includes the automated landing system. The localizer deviation is an indication of the aircraft's position relative to the desired path to the runway centerline. For example, the localizer deviation may indicate the aircraft is approximately 2° left of the runway centerline. The glideslope deviation is an indication of the aircraft's position relative to the desired glideslope to the runway. For example, the glideslope deviation may indicate the aircraft is 1° below the desired glideslope. The flight control module uses the localizer deviation and the glideslope deviation to adjust the automated landing system and to command control surfaces of the aircraft.
Many known automated landing systems require three independently computed localizer and glideslope deviations. Such redundancy ensures that if one localizer deviation or one glideslope deviation fails, the automated landing system still has two good signals to control the aircraft. The redundant equipment necessary for independently computing three localizer and glideslope deviations adds cost and weight to the aircraft. If the available localizer deviation and glideslope deviations disagree beyond a predetermined threshold, the automated landing system forfeits control of the aircraft to the pilot. The availability of reliable, i.e., “good,” localizer deviation and glideslope deviation signals is particularly important when the aircraft descends below 200 feet, because the margins for error are tighter and errant control by the automated landing system may result in the aircraft missing the runway. Accordingly, when failures or erroneous localizer or glideslope signals are detected, the flight control system relies on the good localizer and glideslope signals or forfeits control to the pilot.